I wouldn't let it bother you too much.
I've spent over a man-day so far cleaning the
copper lining out of a Garand I recently procured. While I think that's not
right, a small amount of barrel cleaning wouldn't have bothered me.
I guess to some, barrel cleaning is just a suggestion.
Look at it like this, if he's really concerned about it, he'll have a remedy
at hand. If it's just going to line his safe, he'll probably pay it no mind.
If he's re-selling it, it's the next person's problem.
(Just the way I see it...)
Personally, keeping my barrels right is nobody's problem but my own.